Electrolysis of anhydrous fused metal chlorides



Patented Mar. 20, 1934 PATENT OFFICE ELECTROLYSIS OF ANHYDROUS FUSED METAL CHLORIDES Karl Staib and Wilhelm Moschel, Bitter-felt], Germany, assignors,

by mesne assignments, to

Magnesium Development Corporation, a corporation of Delaware No Drawing. Application April 7. 1931, Serial No. 528,452. In Germany November 12, 1930 2 Claims.

The present invention relates to improvements in the electrolysis of anhyd ous fused metal chlorides. The invention ismore particularly concerned with processes in which chlorine, re-

sulting from the electrolytic decomposition of anhydrous fused metal chlorides, is utilized in the preparation of further quantities of electrolyte from suitable raw materials.

Processes are known for obtaining fused metal In chlorides, for instance, magnesium chloride, in an anhydrous state and in a form suitable for electrolysis, by causing thecorresponding metal oxides to react with chlorine in presence of carbon or by dehydrating the water-containing 1.; chlorides by treatment with chlorine. It has also been proposed to employ the chlorine produced at-the anode in the electrolysis of such molten chlorides for the conversion of the raw materials into anhydrous chlorides.

We have observed, for example, in the electrolytic production of magnesium metal, that the chlorine gas produced in the anode chamber of the bath by the electrolysis of a melt containing magnesium chloride always carries along a. certain amount of chlorides, especially when the anode chamber is constructed so as to be suited for the recovery of concentrated chlorine. The presence of these chlorides in the chlorine gas is partly due to the evaporation and splashing of the electrolyte. Besides, the chlorine also contains variable amounts of evaporated aluminium chloride and iron chloride. The latter may already be present in the electrolyte from the very beginning in small amounts as impurities or they may be produced during electrolysis by the action of the chlorine on the ash-particles of the carbon electrodes or also on the refractory walls of the anode chamber.

When using chlorine gas contaminated by such foreign metal chlorides in the preparation of anhydrous magnesium chloride for purposes of electrolysis by the methods mentioned above, we have observed that these contaminations are again incorporated in said magnesium chloride and thus, upon introduction of the latter into the electrolytic bath, caused to accumulate in the electrolyte to a continually increasing extent. Under thesecircumstances, they produce a detrimental action, since they are, when present 30 in sufficient amount, reduced by the magnesium liberated at the cathode with the formation of particles of aluminium and iron which particles,

in their turn, sink to the bottom of the bath, causing part of the'molten magnesium produced by the electrolysis to adhere to them and pass with them into the electrolyte sludge, so that ultimately the yield of magnesium is noticeably impaired.

According to our present invention, the said impurities are removed from the chlorine liber- 60 ated at the anode before such chlorine is reutilized for the preparation of anhydrous magnesium chloride. This may be accomplished by causing the chlorine gas to pass, after the con version of the volatile chloride vapours into the 55 form of dust which occurs in the course of the cooling of the chlorine, through a mechanical dust filter, for instance, of asbestos bags, or through an electric filter of the type usually employed in the purification of gases, if neces- 7o sary after having passed the gas through a flue dust canal. After having undergone such purification, the chlorine gas is employed in the conversion of magnesium oxide or similar compounds into anhydrous magnesium chloride, or in thedehydration of hydrated magnesium chloride in the manner known per 'se and outlined above, whereupon the resulting pure anhydrous magnesium chloride is, introduced into the electrolytic bath and subjected to electrolysis.

In the foregoing, the present invention has been described as applied to the manufacture of magnesium metal from a bath containing anhydrous magnesium chloride, but we wish it to be understood that we do not limit the scope of, 35 our invention to such application as the invention will prove advantageous in the production of allother metals, such as calcium and the like, which are obtained by electrolysis of their anhy drous fused chlorides. provided a similar acon cumulation of undesirable impurities such as aluminium and iron compounds is caused in the electrolyte by the circulation of the chlorine.-

We claim:

1. A continuous cyclic process for the electrolytic production of metals from metal oxides involving the electrolysis of the corresponding anhydrous metal chlorides, which comprises recovering the chlorine gas evolved at the anode during such electrolysis, freeing said chlorine gas chlorine gas evolved at the anode during such electrolysis, freeing said chlorine gas from foreign metal chlorides contained therein, reacting the purified chlorine gas with fresh amounts of magnesium oxide so as to form anhydrous magnesium chloride, and subjecting such chloride to electrolysis to produce further amounts of magnesium metal and chlorine gas.

KARL STAIB. WILHELM MOSCHEL. 

